Mendel 2


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Mendel 2

  1. 1. More of Mendel pp. 270 - 274
  2. 2. What we know… <ul><li>Inheritance of biological characteristics is determined by genes </li></ul><ul><li>Principle of Dominance </li></ul><ul><ul><li>When there are two or more alleles for a gene, some are dominant while others are recessive </li></ul></ul><ul><li>Law of Segregation </li></ul><ul><ul><li>In sexually reproducing organisms, adult cells have two copies of each gene—one from each parent; these genes segregate when GAMETES are formed </li></ul></ul>
  3. 3. Does the segregation of 1 pair of alleles affect the segregation of another pair of alleles?
  4. 4. <ul><li>Make a test cross of: </li></ul><ul><ul><li>True breeding Round Yellow Peas </li></ul></ul><ul><ul><ul><li>Genotype (RRYY) </li></ul></ul></ul><ul><ul><li>True breeding Wrinkled Green peas </li></ul></ul><ul><ul><ul><li>Genotype (rryy) </li></ul></ul></ul>RY RY RY RY ry ry ry ry
  5. 5. <ul><li>What is the phenotype of the F1 offspring? </li></ul><ul><li>What is the genotype of the F1 offspring? </li></ul>
  6. 6. What this first cross told us… <ul><li>All F1 offspring were heterozygous for seed shape (round) and seed color (yellow) RrYy </li></ul><ul><li>The F1 plant was made from fusing a gamete carrying RY and a gamete carrying ry </li></ul><ul><li>Will the dominant alleles stay together or separate when making the F2 offspring? </li></ul>
  7. 7. Now cross these hybrid (RrYy) plants on a new 4X4 Punnett Square
  8. 9. What does the F2 cross tell us? <ul><li>Are there combinations of alleles that we did not see in either of the parents? </li></ul><ul><li>This means that the alleles for seed color separated separately than the alleles for seed shape </li></ul><ul><li>Genes that segregate separately do NOT influence each other’s inheritance </li></ul>
  9. 10. Principle of Independent Assortment <ul><li>Genes for different traits can segregate independently during the formation of gametes. This principle helps account for many genetic variations in plants, animals and other organisms. </li></ul>
  10. 11. Mendel’s 4 Principle’s <ul><li>Inheritance of biological characteristics is determined by genes </li></ul><ul><li>Principle of Dominance </li></ul><ul><li>Law of Segregation </li></ul><ul><li>Principle of Independent Assortment </li></ul>
  11. 12. Exceptions to Mendel <ul><li>Genetics more complicated </li></ul><ul><li>Some alleles are neither dominant nor recessive </li></ul><ul><li>Many traits are controlled by multiple alleles or multiple genes </li></ul>
  12. 13. Incomplete Dominance <ul><li>When red flowered (RR) plants were crossed with white flowered (WW) plants they made…pink flowers (RW) </li></ul><ul><li>Which allele is dominant? </li></ul><ul><ul><li>neither </li></ul></ul><ul><li>Incomplete dominance: </li></ul><ul><ul><li>Case in which one allele is not dominant over another </li></ul></ul><ul><ul><li>The heterozygous phenotype is somewhere between the two homozygous phenotypes </li></ul></ul>
  13. 15. Codominance <ul><li>Both alleles contribute to the phenotype </li></ul><ul><li>Chickens </li></ul><ul><ul><li>Allele for black feathers is codominant with allele for white feathers </li></ul></ul><ul><ul><li>Chicken looks speckled with black and white feathers </li></ul></ul><ul><ul><li>Not like the blending of dominant phenotypes… </li></ul></ul><ul><ul><li>BOTH dominant phenotypes show up </li></ul></ul><ul><li>In humans </li></ul><ul><ul><li>Gene for protein that controls cholesterol levels in the blood </li></ul></ul><ul><ul><li>People with heterozygous form make both types of protien </li></ul></ul>
  14. 17. Multiple Alleles <ul><li>When a gene has more than two alleles </li></ul><ul><li>NOT more than 2 alleles for a person but MORE than 2 alleles for the trait exist </li></ul><ul><li>Coat color in rabbits </li></ul><ul><ul><li>A single gene for coat color </li></ul></ul><ul><ul><li>At least 4 different alleles </li></ul></ul><ul><ul><li>Simple dominance and make 4 possible coat colors </li></ul></ul><ul><li>Genes for human blood type </li></ul>
  15. 19. Polygenic Traits <ul><li>“ Poly” many </li></ul><ul><li>“ -genic” genes </li></ul><ul><li>Traits controlled by two or more genes </li></ul><ul><li>Several genes interact to produce a trait </li></ul><ul><li>Wide range of phenotypes </li></ul><ul><li>Skin color </li></ul><ul><ul><li>Four different genes </li></ul></ul><ul><li>Fruit Fly eye color </li></ul><ul><ul><li>Three genes make the reddish brown pigment </li></ul></ul>
  16. 20. Applying Mendel’s Principles… <ul><li>Apply Mendel’s Principles to many organisms, including humans </li></ul><ul><li>Thomas Hunt Morgan (1900’s) </li></ul><ul><ul><li>American geneticist </li></ul></ul><ul><ul><li>Common fruit fly </li></ul></ul><ul><ul><ul><li>Drosophilia melanogaster </li></ul></ul></ul><ul><ul><ul><li>Produced offspring very quickly </li></ul></ul></ul><ul><ul><ul><li>Single pair of flies=100 offspring </li></ul></ul></ul><ul><li>Mendel’s principle’s were tested with Drosophilia and many other organisms and they applied to all of them as well </li></ul>
  17. 21. Genes and the Environment <ul><li>Genes provide the plan for development </li></ul><ul><li>How the plan unfolds depends on the environment </li></ul><ul><li>Example: </li></ul><ul><ul><li>Sunflower has genes for height and color of flowers </li></ul></ul><ul><ul><li>But these traits are also influenced by climate, soil conditions and water availability </li></ul></ul>